life is transient; life is uncertain; memento mori
A set phrase expressing the impermanence of life, often used in reflective or literary contexts. It conveys that one may be here today but gone tomorrow.
Since life is uncertain, I want to live each day with care.
one's days are numbered; one's time is nigh
Used when someone's death is imminent or expected soon, often with a somber or fatalistic tone. More concrete than the general transience sense.
The doctor didn't say it outright, but it seems my days are numbered.
A Buddhist term meaning 'all things are impermanent', more philosophical and less personal than 今日あって明日ない身.
Literally 'tomorrow's life', used in phrases like 明日の命も知れない to express uncertainty of life, similar in meaning but less fixed as an idiom.
A classical Japanese idiom composed of 今日 (today), あって (exist), 明日 (tomorrow), ない (not exist), and 身 (body/self). The exact origin is uncertain, but it reflects a traditional awareness of life's fragility.